The Australian spy agency offered to share the information with the NSA, according to the Times story.

"The attorney-client privilege is a bedrock principle of our free society," ABA President James Silkenat wrote. "The interception and sharing of attorney-client privileged communications by government agencies -- or any third party -- raises concerns, including chilling the full and frank discussion between lawyer and client that is essential for effective legal representation."

Silkenat asked the NSA to explain its policies designed to protect attorney-client privilege. "We know that NSA, as a federal agency committed to the rule of law, recognizes the attorney-client privilege," he wrote.

An NSA spokeswoman didn't have an immediate comment on the ABA letter, but she disputed reports that the NSA has used foreign spy partners to collect information that it cannot.

"Any allegation that NSA relies on foreign partners to circumvent U.S. law is absolutely false," she said by email. "The National Security Agency does not ask its foreign partners to undertake any intelligence activity that the U.S. government would be legally prohibited from undertaking itself."

The NSA works with several partners, but the information collected must be "in support of a valid foreign intelligence requirement, and comply with U.S. attorney general-approved procedures to protect privacy rights," she added.

Attorney-client communications do not get special protections from NSA surveillance, the New York Times article noted.

Grant Gross covers technology and telecom policy in the U.S. government for The IDG News Service. Follow Grant on Twitter at GrantGross. Grant's email address is grant_gross@idg.com.